5 Nuclear physics (5.1 -5.2.2) Flashcards
structure of an atom
a positively charged nucleus and negatively
charged electrons in orbit around the nucleus
how may atoms form positive ions?
by losing electrons
how may atoms form negative ions?
by gaining electrons
relative charges of protons, neutrons, and electrons
proton: +1
neutron: 0
electron: -1
proton number/atomic number
number of protons in the nucleus
(number of protons in a neutral atom should be the same as number of electrons)
mass number/nucleon number
sum of the number of protons and neutrons in the nucleus
Nuclides
type of atom with a specific number of neutrons and protons
nuclide notation
chemical symbol: X
proton number Z
nucleon number: A
to find number of neutrons
nucleon number - proton number
isotope
are atoms of the same element that have equal number of protons but a different number of neutrons
why do isotopes tend to be more unstable?
due to their imbalance of protons nad neutrons
- more likely to decay to achieve stability
How does rutherford’s experiement provide evidence for:
a very small nucleus surrounded by mostly empty space
A majority of them go through the atom, because the atom is mostly empty space
While a very small number are deflected back because the nucleus is very small
How does rutherford’s experiement provide evidence for:
A nucleus containing most of the mass of the atom
Some of the a-particles scattered back, caused by the small, dense nucleus
How does rutherford’s experiement provide evidence for:
A nucleus that is positively charged
Some alpha particles are deflected through small atoms
Happens because the positive alpha particles are repelled by the positive nucleus which contains most of the mass
Rutherford’s experiment procedure
Scattering of alpha particles by a sheet of thin metal
(Expected - alpha particles to travel through the gold foil and maybe change direction a small amount)
Results of rutherford’s experiment
- most of the alpha particles PASSED STRAIGHT THROUGH the foil
- some of the alpha particles CHANGED DIRECTION but continued through the foil
- a few of the alpha particles BOUNCED BACK off the gold foil
ionisation
the addition or removal of an electron from an atom
Nuclear fission
the splitting of a large, unstable nucleus into two smaller nuclei
Nuclear fission process
a neutron collides with an unstable nucleus, causing the nucleus to split into two smaller nuclei (daughter nuclei) as well as two or three neutrons
- gamma rays are emitted
How to know if an nuclide equation is fission
there’s a neutron on the left and two daughter nuclei on the right
Nuclear fusion
when two light nuclei join to form a heavier nucleus
why is nuclear fusion hard to reproduce on earth
requires extremely high temperatures to maintain
- happens in stars
Example of a nuclear fusion equation
Two hydrogen nuclei fusing to form a helium nucleus
where does the energy for nuclear fusion come from
a very small amount of the particles mass is being converted to energy
- E = mc^2
(energy = mass x speed of light squared)
background radiation
the radiation that exists around us at all times
sources that make a significant contribution to background radiation
a) radon gas (in the ari)
b) rocks and buildings
c) rood and drink
d) cosmic rays
How can ionising radiation be measured
using a detector connected to a counter
what is count rate
number of decays per second (counts/s)
Examples of devices used to measure ionising radiation
Geiger-Muller tube (or GM tube)
Photographic film
Ionisation chamber
scintillation counters
spark counters
Issues using radioactive isotopes with long half lives to release energ
ECONOMIC
- high cost of storage
- reduction in touirsm
- loss of farming produce
- reduction of land
SOCIAL
- fear of cancer
- sickness in people/animals
ENVIRONMENTAL
- crop mutation
- leakage into water supplies
when is an atom unstable?
when it doesn’t have enough binding energy to hold the nucleus together permanently due to the imbalance of neutrons and protons
Describe the emission of radiation
spontaneous and random in direction
Alpha particles (what, charge, range, penetration and ionisation)
What: helium nucleus (2 protons and 2 neutrons)
Charge: 2+
Range in air: few cm
Penetration: stopped by paper
Ionisation: High
Beta particles (what, charge, range, penetration and ionisation)
What: fast-moving electron
Charge: -1
Range in air: few 10s of cm
Penetration: stopped by as few mm of aluminium
Ionisation: medium
Gamma rays (what, charge, range, penetration and ionisation)
What: EM wave
Charge: 0
Range in air: infinite
Penetration: REDUCED by a few mm of lead
Ionisation: low
What do ionising effects depend on
Kinetic energy and Electric charge
How does kinetic energy affect the ionisation effect?
Higher the kinetic energy of the raidaiton, the more ionising it is
- alpha has highest mass and is most ionising (think 1/2mv^2)
How does electric charge affect the ionisation effect?
Greater the charge the more ionising
- alpha has largest charge and is most ionising
Alpha particles and ionising effect
Most ionising : they leave a dense trail of ions behind them, affecting virtually every atom they meet, because of this they lose their energy and so have a short range
(short range = relatively harmlessm but dangerous if ingested)
When will a particle be deflected in an electric field
if it has charge
(so not gamma)
When will a particle be deflected in a magnetic field
if it has charge and is moving perpendicular to it
Alpha particles are deflected towards what (magnetic field)
the negative plate as they have a positive charge
Beta particles are deflected to what (magnetic filed)
positive plate as they have negative charge
Gamma rays are deflected to what (magnetic field)
Not deflected, travels straight between the plates as they have no charge
Why are alpha particles deflected less (and travel further) than beta particles in magnetic fields
Alpha particles are heavier than beta particles
radioactive decay
change in an unstable nucleus that can result in the emission of alpha particles or beta particles or gamma radiation
- changes are spontaneous and random
what happens to the nucleus during alpha or beta decay
the nucleus changes to that of a different element
define half life (of a particular isotope)
the time taken for half the nuclei of that isotope in any sample to decay
